BLACKSBURG, Va., March 11 (UPI) — A U.S. researcher said women’s marathon running times are affected by poor air quality.

Civil and environmental engineer Lynsey Marr of Virginia Polytechnic Institute in Blacksburg said higher levels of pollution particles in the air were associated with slower running times for women. However, men were not significantly affected.

Marr suggests the gender difference may be due to the smaller size of women’s trachea’s, which makes it easier for particles to deposit there and possibly cause irritation.

Marr and Matthew Ely of the U.S. Army Research Institute of Environmental Medicine evaluated marathon race results, weather data and air pollutant concentrations in seven marathons held in major U.S. cities, including New York and Los Angeles, over a period of eight to 28 years.

“Although pollution levels in these marathons rarely exceeded national standards for air quality, performance was still affected,” Marr said in a statement.

Previous research has shown marathon runners during a race inhale and exhale about the same volume of air as a sedentary person would over the course of two full days.